Carpenter ants of the Brazilian rain forest have it rough. When one of these insects gets infected by a certain fungus, it turns into a so-called “zombie ant” and is no longer in control of its actions. Manipulated by the parasite, an infected ant will leave the cozy confines of its arboreal home and head to the forest floor—an area more suitable for fungal growth. After parking itself on the underside of a leaf, the zombified ant anchors itself into place by chomping down onto the foliage. This marks the victim’s final act. From here, the fungus continues to grow and fester inside the ant’s body, eventually piercing through the ant’s head and releasing its fungal spores. This entire process, from start to finish, can take upwards of ten agonizing days.

A dead spiny ant with fungal spores erupting out of it's head.

“We found that a high percentage of the cells in a host were fungal cells,” said Hughes. “In essence, these manipulated animals were a fungus in ants’ clothing.”

We’ve known about zombie ants for quite some time, but scientists have struggled to understand how the parasitic fungus, O. unilateralis (pronounced yu-ni-lat-er-al-iss), performs its puppeteering duties. This fungus is often referred to as a “brain parasite,” but new research published this week in Proceedings of the National Academy of Sciences shows that the brains of these zombie ants are left intact by the parasite, and that O. unilateralis is able to control the actions of its host by infiltrating and surrounding muscle fibers throughout the ant’s body. In effect, it’s converting an infected ant into an externalized version of itself. Zombie ants thus become part insect, part fungus. Awful, right?

To make this discovery, the scientist who first uncovered the zombie ant fungus, David Hughes from Penn State, launched a multidisciplinary effort that involved an international team of entomologists, geneticists, computer scientists, and microbiologists. The point of the study was to look at the cellular interactions between O. unilateralis and the carpenter ant host Camponotus castaneus during a critical stage of the parasite’s life cycle—that phase when the ant anchors itself onto the bottom of leaf with its powerful mandibles.

“The fungus is known to secrete tissue-specific metabolites and cause changes in host gene expression as well as atrophy in the mandible muscles of its ant host,” said lead author Maridel Fredericksen, a doctoral candidate at the University of Basel Zoological Institute, Switzerland, in a statement. “The altered host behavior is an extended phenotype of the microbial parasite’s genes being expressed through the body of its host. But it’s unknown how the fungus coordinates these effects to manipulate the host’s behavior.”

By referring to the parasite’s “extended phenotype,” Fredericksen is referring to the way that O. unilateralis is able to hijack an external entity, in this case the carpenter ant, and make it a literal extension of its physical self.

For the study, the researchers infected carpenter ants with either O. unilateralisor a less threatening, non-zombifying fungal pathogen known as Beauveria bassiana, which served as the control. By comparing the two different fungi, the researchers were able to discern the specific physiological effects of O. unilateralis on the ants.

Using electron microscopes, the researchers created 3D visualizations to determine location, abundance, and activity of the fungi inside the bodies of the ants. Slices of tissue were taken at a resolution of 50 nanometers, which were captured using a machine that could repeat the slicing and imaging process at a rate of 2,000 times over a 24-hour period. To parse this hideous amount of data, the researchers turned to artificial intelligence, whereby a machine-learning algorithm was taught to differentiate between fungal and ant cells. This allowed the researchers to determine how much of the insect was still ant, and how much of it was converted into the externalized fungus.

truly disturbing. Cells of O. unilateralis had proliferated throughout the entire ant’s body, from the head and thorax right down to the abdomen and legs. What’s more, these fungal cells were all interconnected, creating a kind of Borg-like, collective biological network that controlled the ants’ behavior.

“We found that a high percentage of the cells in a host were fungal cells,” said Hughes in a statement. “In essence, these manipulated animals were a fungus in ants’ clothing.”

But most surprising of all, the fungus hadn’t infiltrated the carpenter ants’ brains.

“Normally in animals, behavior is controlled by the brain sending signals to the muscles, but our results suggest that the parasite is controlling host behavior peripherally,” explained Hughes. “Almost like a puppeteer pulls the strings to make a marionette move, the fungus controls the ant’s muscles to manipulate the host’s legs and mandibles.”

As to how the fungus is able to navigate the ant towards the leaf, however, is still largely unknown. And in fact, that the fungus leaves the brain alone may provide a clue. Previous work showed that the fungus may be chemically altering the ants’ brains, leading Hughes’ team to speculate that the fungus needs to the ant to survive long enough to perform its final leaf-biting behavior. It’s also possible, however, that the fungus needs to leverage some of that existing ant brain power (and attendant sensorial capabilities) to “steer” the ant around the forest floor. Future research will be required to turn these theories into something more substantial.

“This is an excellent example of how interdisciplinary research can drive our knowledge forward,” Charissa de Bekker, an entomologist at the University of Central Florida not affiliated with the new study, told Gizmodo. “The researchers used cutting-edge techniques to finally confirm something that we thought to be true but weren’t sure about: that the fungus O. unilateralis does not invade or damage the brain.”

de Bekker says this work confirms that something much more intricate is going on, and that the fungus might be controlling the ant by secreting compounds that can work as neuromodulators. Data gleaned from the fungal genome points to this conclusion as well.

“This means the fungus might produce a wealth of bioactive compounds that could be of interest in terms of novel drug discovery,” said de Bekker. “I am, thus, very excited about this work!”

An authority on the zombie ant fungus herself, de Bekker also released new research this week. Her new study, published in PLOS One and co-authored with David Hughes and others, looked into the molecular clock of the Ophiocordyceps kimflemingiae fungus (a recently named species of the O. unilateralis complex) to see if the daily rhythms, and thus biological clocks, are an important aspect of the parasite-host interactions studied by biologists.

“In addition to confirming that the fungus indeed has a molecular clock, we found that this results in the daily oscillation of certain genes,” de Bekker told Gizmodo. “While some of them are active during the day-time, others are active during the night-time. Interestingly, we found that the fungus especially activates genes encoding for secreted proteins during the night-time. These are the compounds that possibly interact with the host’s brain! The fungus, therefore, does not just release bioactive compounds to manipulate behavior, but there seems to be a precise timing to it as well.”

There’s clearly still lots to learn about this insidious parasite and how it hijacks its insectoid hosts, but as these recent studies attest, we’re getting steadier closer to the answer—one that’s clearly disturbing in nature.

[Proceedings of the National Academy of Sciences, PLOS One]

I see your love shining out from my furry friends faces, when I look into their eyes. I see you in the flower’s smile, the rainbow, and the wind in the trees....

This info on fungus gives a whole new spin to the concept of cultures! I might be terrified by the fungus amungus if I did not have a CERTAINTY that I am not just a body on a planet ruled by mycellium. AND at the same time we have this zombie horror, in other places, other (uplifting) cultures demonstrate altruism that looks familiarly comforting:

“This means the fungus might produce a wealth of bioactive compounds that could be of interest in terms of novel drug discovery,” said de Bekker. “I am, thus, very excited about this work!”

I found that single line to be the most disturbing.

I was also provoked by the line "ten agonizing days" to wonder if ants feel pain. Following that lead I found an article with a photo of another of our enigmatic insect friends, it's funny enough to post here.

There is such wonder in the natural world where everything reflects a total state of being ... Kind of strange to see the article's title using the words diabolical and zombies... I found the transference to human emotionally charged words odd.

The journey, the challenge is to step into the
projection room and stop being lost in the script.

Love those videos you posted Maggie! There probably is more HFW things going on in the animal kingdom of this sort than we know. I never have my camera handy nor do I ever think about video. It's too bad, because I have had some amazing moments where I wished I did. With a combination of dogs, goats, cats, and a horse right out our main front window I get to see a lot of funny things when they don't know I'm watching. I often wonder whether animals behavior is actually changing, or if we were all so programmed that we just didn't notice how amazing, even kind and compassionate, and incredibly intelligent they can be.

I did mainly post that article about ants because it was shocking to me. And especially what Christine highlighted in her post, about their choice of wording for the title even. What's the deal with the zombie meme? I don't find it attractive. In fact, quite the opposite. I'm not against all insects, as they are an important part of how things work here, and some I actually like. We have quite an assortment out here. I'm always happy when I see bees frequenting the garden, but the yellow jackets can be downright mean, and are very carnivorous. I don't like it when they try to take a bite out of me. And then we have these beetles. We all call them pine bugs, because they stink when you mess with them, and it's not the good kind. Many of these varieties are harmful to trees. But then we have a ridiculously large population of turkeys out here, and they happen to eat them! So nature is always trying to establish a balance.

But I've also had some weird memories, visions, and dreams concerning insectoids. I used to think praying/preying mantises were cool, but kind of don't like them anymore. And I had a horrible nightmare when I was a kid about ants that left me shaken for quite some time afterwards. Then I had another dream about creepy black spiders coming in through the ceiling. In this same dream I had another type of insect come up from within a deep well that went a long ways down into the earth. This bug sang a beautiful melody and had a completely different feel to it. As usual, it's all about learning discernment. It's not just how something looks, it's also how it feels.

I see your love shining out from my furry friends faces, when I look into their eyes. I see you in the flower’s smile, the rainbow, and the wind in the trees....